Michelle Walvoord, of the New Mexico Institute of Mining and Technology, spoke to the geology department about desert water table dynamics on March 15. Her talk, titled "Desert Vadose Zones: re-supply or refuse?," outlined her work in the field, which includes formulating a new model for water flow and aquifer recharge in arid and semi-arid regions. Vadose zones are the regions between the surface of the ground and the water table. The flow of water in these zones is important in the issue of storage of nuclear waste in the deserts of the Southwest.
"The problem with past hypotheses regarding water flow in arid regions is the application of the model from humid climates to arid ones. The two climates are very different, and different models must be applied to each." Past models say that what little water exists in the arid vadose zone seeps from the surface down to the water table 50-500m below the surface. Walvoord's new model argues that plants adapted to the arid conditions trap water in their roots and create a wicking phenomenon, causing upward travel of some water.
"The change in vegetation structure from forest to scrubland at the Pleistocene-Holocene boundary has altered the hydrologic character of the vadose zone in these now arid regions. The desert plants conserve more water in their roots." The implication for the desert as a dumping place for nuclear waste is that plant suction could potentially prevent the contamination of ground water. These plants must be in place to maintain suction however, and the digging required to bury the waste would remove the native flora at the site. Replanting of indigenous plants may be a possibility to ensure the safety of these sites.
Michelle Walvoord is a candidate for a visiting professorship in geology for the 2002-2003 school year.
